This invention relates to a target for the production of Mo-99 fission product and for a method of preparing the target. The radioisotope Mo-99 is useful in the medical sciences as a source of Tc-99m, a diagnostic tool. Tc-99m is well suited for radiometric scanning of internal organs due to its short half-life resulting in reduced radiation exposure in medical applications. Ordinarilly, the users of Tc-99m will maintain a supply of Mo-99 from which Tc-99m can be extracted as required.
Previously, Mo-99 sources have been prepared by separating fission product Mo-99 from irradiated uranium highly enriched targets or by the irradiation of naturally occuring molybdenum. In the later case, only a small fraction of the molybdenum is converted to radioisotope Mo-99 such that the specific activity of the source is very low.
Uranium targets, including uranium oxide, with a high enrichment of uranium 235, i.e. in excess of 90%, have been irradiated for the production of fission product Mo-99. High purity Mo-99 can be separated from the remaining fission products and transuranium elements by well established techniques. However, the uranium targets with high enrichment must be handled with extreme care under carefully regulated conditions with heavy restrictions on their distribution.
Representive techniques for the production of Mo-99 as a source of Tc-99 are described in U.S. Pat. No. 3,940,318 to Arino et al. and U.S. Pat. No. 3,799,883 to Arino et al. U.S. Pat. No. ('318) describes a target and process for irradiating highly enriched uranium for the production of Mo-99 fission product. The uranium target material is electrodeposited as uranium oxide from aqueous solution containing uranyl compounds onto a stainless steel substrate. The separation of Mo-99 from other fission products, residual uranium and transuranium products in described in U.S. Pat. No. ('883).
Although uranium metal along with transuranium elements have been electrorefined from molten salt mixtures (e.g. U.S. Pat. No. 4,596,647), considerable difficulties have been encountered in obtaining good bonding of uranium deposits to corrosion resistant substrates such as stainless steels and zirconium alloys. Futhermore, electroplated uranium metal has exhibited extensive dendrite formations which impair its suitability as a target material.
Therefore, in view of the above, it is an object of the present invention to provide an improved target for the production of Mo-99.
It is also an object to provide a uranium target with a low enrichment of uranium-235 for Mo-99 production.
It is a further object to provide an irradiation target which exhibits good bonding of low enriched uranium metal to a target substrate surface.
It is also an object of the present invention to provide a method for the deposition of uranium metal with a low enrichment of uranium-235 onto a substrate to form a well-bonded layer of dendrite-free uranium.
It is likewise an object of the present invention to provide a method of producing an irradiation target with sufficient uranium density to be compatable with current target and irradiation configurations for the production of the fission product, Mo-99.